Crystal growing method for crystals

ABSTRACT

A crystal growing method for crystals include the following steps. A first crystal seed is provided, the first crystal seed has a first monocrystalline proportion and a first size. N times of crystal growth processes are performed on the first crystal seed, wherein each of the crystal growth process will increase the monocrystalline proportion, and the N times of crystal growth processes are performed until a second crystal having a monocrystalline proportion of 100% is reached, and wherein the N times includes more than 3 times of crystal growth processes. Each crystal growth process includes adjusting a ratio difference (ΔTz/ΔTx) between an axial temperature gradient (ΔTz) and a radial temperature gradient (ΔTx) of the crystal, so as to control the ratio difference within a range of 0.5 to 3 for forming the second crystal.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefits of U.S. provisionalapplication Ser. No. 63/359,203, filed on Jul. 8, 2022, U.S. provisionalapplication Ser. No. 63/359,205, filed on Jul. 8, 2022, and U.S.provisional application Ser. No. 63/359,208, filed on Jul. 8, 2022. Theentirety of the above-mentioned patent application is herebyincorporated by reference herein and made a part of this specification.

BACKGROUND Technical Field

The present disclosure relates to a crystal growing method for crystals,in particular relates to a crystal growing method for crystals having ahigh monocrystalline proportion and a large size.

Description of Related Art

At present, silicon wafers have been widely used in the semiconductorindustry. Many electronic devices contain silicon wafers produced usingsilicon wafers as materials. However, in order to improve waferperformance, many manufacturers have attempted to use silicon carbidewafers as materials for producing silicon carbide chips. Silicon carbidewafers have the advantages of high temperature resistance and highstability.

As far as the prior art is concerned, it takes a very long time toexpand the diameter of silicon carbide crystals, and it takes severalyears to complete the enlargement of conventional crystals from 6 inchesto 8 inches. In addition, traditional crystal growth methods cannoteffectively form crystals with a high monocrystalline proportion in ashort period of time. Based on the above, how to produce large-sizedcrystals with a high monocrystalline proportion in a shortened time is aproblem to be solved.

SUMMARY

The invention provides a crystal growing method for crystals, which cangreatly shorten the time for forming crystals having a highmonocrystalline proportion and a large size.

The crystal growing method for crystals of the present disclosureincludes the following steps. A first crystal seed is provided, thefirst crystal seed has a first monocrystalline proportion and a firstsize. N times of crystal growth processes are performed on the firstcrystal seed, wherein each of the crystal growth process will increasethe first monocrystalline proportion, and the N times of crystal growthprocesses are performed until a second crystal having a monocrystallineproportion of 100% is reached, and wherein the N times includes morethan 3 times of crystal growth processes.

In one embodiment of the present disclosure, each of the N times ofcrystal growth processes includes adjusting a ratio difference (ΔTz/ΔTx)of an axial temperature gradient (ΔTz) and a radial temperature gradient(ΔTx) of the crystals to control the ratio difference within a range of0.5 to 3 for forming the second crystal.

In one embodiment of the present disclosure, each of the N times ofcrystal growth processes includes the following steps. A previouslyobtained crystal seed is used for crystal growth to obtain anintermediate crystal with increased monocrystalline proportion; when itis confirmed that the monocrystalline proportion of the intermediatecrystal is not 100%, the intermediate crystal is sliced to obtain agrowth crystal seed, wherein the growth crystal seed is used as acrystal seed for a subsequent crystal growth process; and when it isconfirmed that the monocrystalline proportion of the intermediatecrystal reached 100%, the crystal growth processes are stopped and thesecond crystal is obtained.

In one embodiment of the present disclosure, the method further includesthe following steps: providing a preliminary crystal seed, thepreliminary crystal seed has a size A and a monocrystalline proportionA′, wherein the size A is smaller than the first size, and themonocrystalline proportion A′ is larger than the first monocrystallineproportion; using the preliminary crystal seed to perform a crystalgrowth process to obtain a first crystal having the first size and thefirst monocrystalline proportion; and slicing the first crystal to formthe first crystal seed.

In one embodiment of the present disclosure, the N times includes morethan 3 times and less than 8 times of crystal growth processes.

In one embodiment of the present disclosure, the N times includes morethan 4 times and less than 6 times of crystal growth processes.

In one embodiment of the present disclosure, each of the crystal growthprocesses has different processing conditions.

In one embodiment of the present disclosure, each of the crystal growthprocesses has a different ratio difference, or different doping amountsof a nitrogen concentration.

In one embodiment of the present disclosure, each of the crystal growthprocesses includes controlling a doping amount of the nitrogenconcentration in a range of 2*10¹⁸ atom/cm³ to 3*10¹⁸ atom/cm³.

In one embodiment of the present disclosure, the first monocrystallineproportion is 70% to 80%.

In one embodiment of the present disclosure, the first size is 200 mm.

Based on the above, by using the crystal growing method of the presentdisclosure for growing silicon carbide crystals, it is possible tosignificantly shorten the time required for forming crystals having ahigh monocrystalline proportion and a large size, and crystals havingexpanded diameter and/or with 100% monocrystalline proportion can beachieved within a certain number of crystal growth processes.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure, and are incorporated in and constitutea part of this specification. The drawings illustrate exemplaryembodiments of the disclosure and, together with the description, serveto explain the principles of the disclosure.

FIG. 1 is a schematic diagram of a crystal growth device according to anembodiment of the present disclosure.

FIG. 2 is a flowchart of a method of growing silicon carbide crystalsaccording to an embodiment of the present disclosure.

FIG. 3A to FIG. 3D are charts illustrating different doping adjustmentmethods for increasing nitrogen concentration in the method for growingsilicon carbide crystals according to an embodiment of the presentdisclosure.

FIG. 4 is a schematic flowchart of a crystal growing method for crystalsaccording to another embodiment of the present disclosure.

FIG. 5 is a schematic flow chart of preparing a first seed crystal usedin the crystal growing method according to an embodiment of the presentinvention.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a schematic diagram of a crystal growth device according to anembodiment of the present disclosure. FIG. 2 is a flowchart of a methodof growing silicon carbide crystals according to an embodiment of thepresent disclosure. Hereinafter, a method of growing silicon carbidecrystals according to some embodiments of the present disclosure will bedescribed with reference to the crystal growth device shown in FIG. 1and the flow chart shown in FIG. 2 .

As shown in FIG. 1 and step S10 of FIG. 2 , in the crystal growthprocess, a raw material 110 including a carbon element and a siliconelement, and a seed crystal 106 above the raw material 110 are providedinto the reactor 102. For example, the raw material 110 is siliconcarbide powder, which is placed at a bottom section of the reactor 102and used as a solid sublimation source. The seed crystal 106 is placedon a top section of the reactor 102. In some embodiments, the seedcrystal 106 can be fixed on a seed crystal loading platform (not shown)by an adhesive layer. The material of the seed crystal 106 includessilicon carbide. For example, the seed crystal 106 is 6H silicon carbideor 4H silicon carbide. In other embodiments, the seed crystal 106includes 6H silicon carbide and 4H silicon carbide.

As shown in FIG. 1 and step S20 of FIG. 2 , in some embodiments, asilicon carbide growth process is performed to form the silicon carbidecrystal 108. For example, the growth process further includes performingstep S22 and step S24. In step S22, the reactor 102 and the raw material110 are heated to form silicon carbide crystals 108 on the seed crystals106. In step S24 of the above growth process, a ratio difference(ΔTz/ΔTx) of an axial temperature gradient (ΔTz) and a radialtemperature gradient (ΔTx) of the silicon carbide crystal 108 isadjusted so that the ratio difference is controlled in the range of 0.5to 3 to form the silicon carbide crystal.

In the above step S22 and step S24, the silicon carbide crystal 108 isformed on the seed crystal 106 by physical vapor transport (PVT). Insome embodiments, the reactor 102 and the raw material 110 are heated bythe induction coil 104 to form the silicon carbide crystal 108 on theseed crystal 106. During the manufacturing process, the seed crystal 106receives the raw material 110 (silicon carbide powder) that issolidified from a gaseous state, and slowly forms semiconductor crystalson the seed crystal 106 until the silicon carbide crystal 108 with thedesired size is obtained. Subsequently, referring to FIG. 1 and step S30of FIG. 2 , after the silicon carbide crystal 108 is grown to a desiredsize, the reactor 102 and the raw material 110 are cooled to obtain asilicon carbide ingot composed of the silicon carbide crystal 108. Insome embodiments, the ingots formed may have different crystallinestructures depending on the orientation of the monocrystalline crystalseed used. For example, silicon carbide ingots include 4H-siliconcarbide, 6H-silicon carbide, and the like. Both 4H-silicon carbide and6H-silicon carbide belong to the hexagonal crystal system.

In the above-mentioned embodiment, when the reactor 102 and the rawmaterial 110 are heated to form the silicon carbide crystal 108, theaxial temperature gradient (ΔTz) refers to the temperature gradient ofthe silicon carbide crystal 108 in the thickness direction, while theradial temperature gradient (ΔTx) refers to the temperature gradient ofthe silicon carbide crystal 108 in a horizontal direction perpendicularto the thickness direction. In some embodiments, the growth ratedifference of each crystal direction is utilized to adjust a temperaturedifference to achieve the ratio difference (ΔTz/ΔTx) in the range of 0.5to 3. In general, a growth rate of the <11-20> crystal orientation isgreater than a growth rate of the <1-100> crystal orientation. In theembodiment of the present disclosure, the growth rates of the twocrystal orientations are controlled to be the same, so that the crystalsin each axial/radial direction can obtain a certain growth rate foradjusting the ratio difference (ΔTz/ΔTx) to be in the range of 0.5 and3.

In some embodiments, the ratio difference (ΔTz/ΔTx) of the axialtemperature gradient (ΔTz) and the radial temperature gradient (ΔTx) iscontrolled in the range of 0.5 to 3 to form the silicon carbide crystal108. In some embodiments, the ratio difference (ΔTz/ΔTx) of the axialtemperature gradient (ΔTz) and the radial temperature gradient (ΔTx) iscontrolled in the range of 2 to 3 to form the silicon carbide crystal108. In some embodiments, the ratio difference (ΔTz/ΔTx) of the axialtemperature gradient (ΔTz) and the radial temperature gradient (ΔTx) iscontrolled in the range of 2.5 to 3 to form the silicon carbide crystal108. In cases where the ratio difference (ΔTz/ΔTx) between the axialtemperature gradient (ΔTz) and the radial temperature gradient (ΔTx) arecontrolled within the above range, the formed silicon carbide crystal108 can have improved uniformity of the resistivity.

In some embodiments, when the reactor 102 and the raw material 110 areheated to form the silicon carbide crystal 108, that is, during thegrowth process of the silicon carbide crystal 108, a doping amount of anitrogen concentration is further increased so that the nitrogenconcentration increases from a first concentration to a secondconcentration. In some embodiments, the first concentration is 2*10¹⁸atoms/cm³, and the second concentration is 3*10¹⁸ atoms/cm³. In someembodiments, the first concentration is 2.2*10¹⁸ atoms/cm³, and thesecond concentration is 2.9*10¹⁸ atoms/cm³. In some embodiments, thefirst concentration is 2.5*10¹⁸ atoms/cm³, and the second concentrationis 2.8*10¹⁸ atoms/cm³. In cases where the doping amount of the nitrogenconcentration is controlled within the above range, the uniformity ofresistivity of the formed silicon carbide crystal can be furtheroptimized.

In the above embodiments, the nitrogen concentration can be increased ina linear fashion or in a stepwise fashion. For example, different dopingadjustment methods of the nitrogen concentration are described withreference to FIG. 3A to FIG. 3D.

FIG. 3A to FIG. 3D are charts illustrating different doping adjustmentmethods for increasing nitrogen concentration in the method for growingsilicon carbide crystals according to an embodiment of the presentdisclosure. As shown in FIG. 3A, in this embodiment, the flow rate ofthe nitrogen gas is increased linearly as compared with time, thus thenitrogen concentration is also increased in a linear fashion. As shownin FIG. 3B, in this embodiment, the flow rate of the nitrogen gas isincreased in a stepwise fashion as compared with time, thus the nitrogenconcentration is also increased in a stepwise fashion. As shown in FIG.3C, in this embodiment, the flow rate of the nitrogen gas is increasedstepwise as compared to time. However, in the embodiment of FIG. 3C, theflow rate of the nitrogen gas is increased directly at the start of theprocess, which is unlike the process shown in FIG. 3B whereby the flowrate of the nitrogen gas is stabilized at 10 seem for a period of timebefore the concentration is increased in a stepwise fashion. As shown inFIG. 3D, in this embodiment, the flow rate of the nitrogen gas isincreased stepwise as compared to the time. However, in the embodimentof FIG. 3D, the amount of the flow rate of the nitrogen gas increased ineach stepwise process is different, and a residence time at specificnitrogen flow rates are also different.

In the embodiment of the present disclosure, increasing the dopingamount of the nitrogen concentration is performed by increasing the flowrate of nitrogen gas in the reactor, so that the increase of the flow ofnitrogen is controlled in the range of 10 sccm to 50 sccm, and themethod shown in the above FIG. 3A to FIG. 3D can be used to increase thenitrogen concentration in a linear or stepwise fashion. In someembodiments, the increase of the nitrogen flow rate is controlled withinthe range of 10 sccm to 30 sccm.

In cases where the above method is used to form silicon carbidecrystals, a monocrystalline proportion of the formed silicon carbidecrystals and the silicon carbide wafers obtained after processing is100%, and the resistivity of silicon carbide crystals/wafers is in arange of 15 mΩ·cm to 20 mΩ·cm, preferably within the range of 19 mΩ·cmto 20 mΩ·cm, and a deviation of an uniformity of the resistivity of thesilicon carbide wafer is less than 0.4%. In some embodiments, thedeviation of the uniformity of the resistivity of the silicon carbidewafer is less than 0.01%. In addition, in some embodiments, basal planedislocations (BPD) of the silicon carbide crystals/wafers is less than200/cm². In some embodiments, basal plane dislocations (BPD) of thesilicon carbide crystals/wafers is less than 140/cm². In someembodiments, a bar stacking fault (BSF) of the silicon carbidecrystals/wafers is less than 5/wafer. Accordingly, a silicon carbidecrystal/wafer with a uniform resistivity distribution can be obtained,and a stress of the formed silicon carbide crystal/wafer is alsolowered, and the geometry of the wafers after processing is alsoimproved.

FIG. 4 is a schematic flowchart of a crystal growing method for crystalsaccording to another embodiment of the present disclosure. In someembodiments, the above silicon carbide crystal growth method can be usedto perform the crystal growing process. As shown in FIG. 4 , in thecrystal growing method of the embodiment of the present disclosure, afirst crystal seed 202 is provided, wherein the first crystal seed 202has a first monocrystalline proportion and a first size. In someembodiments, the first monocrystalline proportion is 70% to 80%, and thefirst size is 200 mm.

As shown in FIG. 4 , a first crystal growth process (N=1) is performedusing the first crystal seed 202 to obtain an intermediate crystal 204with an increased monocrystalline proportion. When it is confirmed thatthe monocrystalline proportion of the intermediate crystal 204 is not100%, the intermediate crystal 204 is sliced to obtain the growthcrystal seed 204A. Subsequently, the previously obtained growth crystalseed 204A can be used as the crystal seed for the next crystal growingprocess. For example, in the second crystal growth process (N=2), thegrowth crystal seed 204A is used to perform the crystal growing process,so as to obtain the intermediate crystal 206 with an increasedmonocrystalline proportion. When it is confirmed that themonocrystalline proportion of the intermediate crystal 206 is not 100%,the intermediate crystal 206 is sliced to obtain the growth crystal seed206A. Accordingly, the crystal growing process can be repeated severaltimes (N=X) until the monocrystalline proportion of the intermediatecrystal formed by the final crystal seed SD1 is 100%, whereby suchintermediate crystal can be designated as the second crystal 250, whichcompletes the crystal growing method in accordance with the embodimentsof the present disclosure.

In the above-mentioned examples, the crystal growth process is performedfor the first crystal seed 202 for N times, wherein each of the crystalgrowth processes will increase the first monocrystalline proportion, andthe N times of crystal growth processes are performed until a secondcrystal 250 having a monocrystalline proportion of 100% is reached. Inother words, when an intermediate crystal having a monocrystallineproportion of 100% is confirmed, the above crystal growth process isstopped to form the second crystal 250. In some embodiments, the N timesincludes more than 3 times of crystal growth processes. In someembodiments, the N times includes more than 3 times and less than 8times of crystal growth processes. In some embodiments, the N timesincludes more than 4 times and less than 6 times of crystal growthprocesses.

Furthermore, in the above embodiments, each crystal growth processincludes adjusting a ratio difference (ΔTz/ΔTx) between an axialtemperature gradient (ΔTz) and a radial temperature gradient (ΔTx) ofthe crystal, so as to control the ratio difference within a range of 0.5to 3. In the above embodiments, each crystal growth processes includescontrolling a doping amount of a nitrogen concentration in a range of2*10¹⁸ atom/cm³ to 3*10¹⁸ atom/cm³. In some embodiments, each of thecrystal growth processes are different. For example, in the embodimentsof the present disclosure, the ratio difference (ΔTz/ΔTx) between anaxial temperature gradient (ΔTz) and a radial temperature gradient (ΔTx)for each of the crystal growth processes are different, and/or thedoping amount of the nitrogen concentration are different, provided thatthe above ratio difference and the doping amount of the nitrogenconcentration are still controlled in the above ranges. By using theabove methods, it is possible to grow from a B-grade seed (lowmonocrystalline proportion) into an A-grade crystal (monocrystallineproportion being 100%) within a certain number of crystal growthprocesses. As such, it is possible to significantly shorten the timerequired for forming crystals having a high monocrystalline proportionand a large size.

FIG. 5 is a schematic flow chart of preparing a first seed crystal usedin the crystal growing method according to an embodiment of the presentinvention. In some embodiments, smaller-sized crystal seeds can also beused in expanding the diameter to form larger-sized crystals. As shownin FIG. 5 , in some embodiments, a preliminary crystal seed PX1 isprovided, wherein the preliminary crystal seed PX1 has a size A and amonocrystalline proportion of A′. In some embodiments, the size A issmaller than the first size of the first crystal seed 202, and themonocrystalline proportion A′ is larger than the first monocrystallineproportion of the first crystal seed 202. For example, when the firstcrystal seed 202 has a first monocrystalline proportion of 70% to 80%and a first size of 200 mm, the single crystal ratio A′ of thepreliminary crystal seed PX1 is 100%, and the size A of the preliminarycrystal seed PX1 is 150 mm.

As shown in FIG. 5 , the preliminary crystal seed PX1 is used forperforming a crystal growth process to obtain a first crystal PX2 havingthe above-mentioned first size and the above-mentioned firstmonocrystalline proportion. In the embodiment of the present disclosure,the crystal growth process of the preliminary crystal seed PX1 includesadjusting the ratio difference (ΔTz/ΔTx) between the axial temperaturegradient (ΔTz) and the radial temperature gradient (ΔTx) of the crystalto control the ratio difference in the range of 0.5 to 3, and to controlthe doping amount of the nitrogen concentration in the range of 2*10¹⁸atoms/cm³ to 3*10¹⁸ atoms/cm³. After the first crystal PX2 is obtained,the first crystal PX2 is sliced to obtain the above diameter-expandedfirst crystal seed 202, and the first crystal seed 202 can be used toperform the steps shown in FIG. 4 to obtain the second crystal 250having a monocrystalline proportion of 100%. By using the above method,it is possible to grow and expand the diameter of an A-grade seed(monocrystalline proportion being 100%) to form an A-grade crystal(monocrystalline proportion being 100%) with a larger size within acertain number of crystal growth processes. As such, it is possible tosignificantly shorten the time required for forming crystals having ahigh monocrystalline proportion and a large size, thus the multipleexpansion steps and years of expansion time required for traditionalcrystal size expansion can be avoided.

EXAMPLES

In order to prove that the method of the present invention can producesilicon carbide crystals with uniform resistivity, and can significantlyshorten the time required for forming large-sized crystals with a highmonocrystalline proportion, the following examples are performed anddescribed.

First Example

In the first example, (i) the ratio difference (ΔTz/ΔTx) between theaxial temperature gradient (ΔTz) and the radial temperature gradient(ΔTx), (ii) the doping variation method of the nitrogen concentration,and (iii) the doping amount of the nitrogen concentration of Examples 1to 7 and Comparative Examples 1 to 4 are adjusted in the mannerdescribed in Table 1 and Table 2 below. Furthermore, the growth processis performed in the manner described in FIG. 1 and FIG. 2 to formsilicon carbide crystals. The evaluation of the basal planedislocations, monocrystalline proportion of the wafer, resistivity ofthe wafer, deviation of an uniformity of the resistivity of the wafer,and bar stacking-fault (BSF) of the obtained silicon carbide wafers arealso shown in Table 1 and Table 2.

TABLE 1 Item Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 (i) ratio difference 0.5 1 2 0.8 1.7 2.5 3 (ΔTz/ΔTx) betweenthe axial temperature gradient (ΔTz) and the radial temperature gradient(ΔTx) (ii) doping From low From low From low From low From low From lowFrom low variation method of to high to high to high to high to high tohigh to high the nitrogen (FIG. 3A) (FIG. 3B) (FIG. 3C) (FIG. 3D) (FIG.3A) (FIG. 3A) (FIG. 3A) concentration (iii) doping Low: Low: Low: Low:Low: Low: Low: amount of the greater than greater than greater thangreater than greater than greater than greater than nitrogen 2 × 10¹⁸2.1 × 10¹⁸ 2.1 × 10¹⁸ 2.2 × 10¹⁸ 2.3 × 10¹⁸ 2.4 × 10¹⁸ 2.5 × 10¹⁸concentration High: High: High: High: High: High: High: (atom/cm³) lessthan less than less than less than less than less than less than 3 ×10¹⁸ 2.9 × 10¹⁸ 2.9 × 10¹⁸ 2.9 × 10¹⁸ 2.8 × 10¹⁸ 2.8 × 10¹⁸ 2.8 × 10¹⁸The obtained silicon carbide wafers: basal plane Less Less Less LessLess Less Less dislocations than 199 than 195 than 187 than 176 than 164than 161 than 145 (BPD)(amount/cm²) Monocrystalline  100%  100%  100% 100%  100%  100%  100% proportion (%) Resistivity 15~20 15~20 18~2018~20 18~20 19-20 19-20 (mΩ · cm) deviation of an <0.4% <0.35% <0.2%<0.15% <0.1% <0.08% <0.01% uniformity of the resistivity (% dev) Barstacking fault 5   3 2 1   2   1   1 (BSF) (ea/wafer)

TABLE 2 Item Comparative Comparative Comparative Comparative Example 1Example 2 Example 3 Example 4 (i) ratio difference 0.4  3  4 0.3(ΔTz/ΔTx) between the axial temperature gradient (ΔTz) and the radialtemperature gradient (ΔTx) (ii) doping Fixed Fixed From low From lowvariation method of concentration concentration to high to high thenitrogen concentration (iii) doping 1 × 10¹⁸ 4 × 10¹⁸ Low: Low: amountof the greater than greater than nitrogen 1 × 10¹⁸ 2 × 10¹⁸concentration High: High: (atom/cm³) less than less than 3 × 10¹⁸ 3.5 ×10¹⁸ The obtained silicon carbide wafers: basal plane Greater GreaterGreater Greater dislocations than 1000 than 1500 than 2500 than 3000(BPD)(amount/cm²) Monocrystalline 100% 100% 100%  100% proportion (%)Resistivity 22~27 22~27 22~27 22~27 (mΩ · cm) deviation of an  >5%  >4% >2% >1.5% uniformity of the resistivity (% dev) Bar stacking fault 32  27 16 10   (BSF) (ea/wafer)

From the experimental results of Examples 1 to 7 shown in Table 1 above,when the ratio difference (ΔTz/ΔTx) between the axial temperaturegradient (ΔTz) and the radial temperature gradient (ΔTx) is controlledin the range of 0.5 to 3, and the doping variation method of thenitrogen concentration is adjusted from low concentration to highconcentration, and when the doping amount of the nitrogen concentrationis controlled in the range of 2*10¹¹ atoms/cm³ to 3*10¹⁸ atoms/cm³, thenthe obtained silicon carbide crystal will have a monocrystallineproportion of 100%, and the silicon carbide wafer obtained afterprocessing can have a uniform resistivity distribution (deviation of theuniformity of the resistivity is less than 0.4%), and the basal planedislocations (BPD) of the wafer can be controlled below 200/cm², the barstacking fault can be controlled to less than or equal to 5/wafer(ea/wf), and the wafer resistivity (15˜20 mΩ·cm) are also within anideal range, and preferably in the range of 19 mΩ·cm to 20 mΩ·cm.

Taking a step further, when the ratio difference (A Tz/A Tx) iscontrolled in the range of 2 to 3, and the doping amount of the nitrogenconcentration is controlled in the range of 2.1*10¹⁸ atoms/cm³ to2.9*10¹⁸ atoms/cm³, then the silicon carbide wafer obtained afterprocessing the silicon carbide crystals has a better uniformity of theresistivity distribution, and less wafer defects and bar stacking faultscan be observed. In addition, when the ratio difference (A Tz/A Tx) iscontrolled in the range of 2.5 to 3, and the doping amount of thenitrogen concentration is controlled in the range of 2.4*10¹⁸ atoms/cm³to 2.8*10¹⁸ atoms/cm³, then the obtained silicon carbide wafer has thebest uniformity of the resistivity distribution, and defects such asbasal plane dislocations (BPD) and bar stacking faults (BSF) are leastobserved. Accordingly, the silicon carbide wafer obtained by processingthe N-type silicon carbide crystals formed by the method of growingsilicon carbide crystals according to the embodiments of the presentdisclosure can have a uniform resistivity distribution, and the crystalstress is low, and the geometry of the processed wafer will also beimproved.

In comparison, from the experimental results shown in Table 2, referringto Comparative Example 1, when the ratio difference (ΔTz/ΔTx) is notcontrolled within the range of 0.5 to 3, and the doping method of thenitrogen concentration is not changed, while a fixed dopingconcentration of 1*10¹⁸ atoms/cm³ is used, the uniformity of theresistivity distribution of the obtained silicon carbide wafer is notgood (deviation of the uniformity >5%), and the basal plane dislocation(BPD) results are also not good. Referring to Comparative Example 2,even when the ratio difference (ΔTz/ΔTx) is controlled within the rangeof 0.5 to 3, if there is no doping variation in the nitrogenconcentration whereby a fixed doping concentration is used, then theuniformity of the resistivity distribution of the obtained siliconcarbide wafer is still not good (deviation of the uniformity >4%), andthe defects such as basal plane dislocations (BPD) and bar stackingfaults (BSF) results are also not good. Referring to ComparativeExamples 3-4, although the doping of the nitrogen concentration isvaried from a low concentration to a high concentration, if the ratiodifference (ΔTz/ΔTx) is not controlled within the range of 0.5 to 3, andif the doping amount of the nitrogen concentration is not controlledwithin the range of 2*10¹⁸ atoms/cm³ to 3*10¹⁸ atoms/cm³, although theuniformity of the resistivity distribution is slightly improved comparedwith Comparative Examples 1-2 (deviation of the uniformity >1.5%), theuniformity of the resistivity distribution is still not within the idealrange, and the defects such as basal plane dislocations (BPD) and barstacking faults (BSF) results are still not good.

Second Example

In the second example, (i) the ratio difference (ΔTz/ΔTx) between theaxial temperature gradient (ΔTz) and the radial temperature gradient(ΔTx), (ii) the doping variation method of the nitrogen concentration,and (iii) the doping amount of the nitrogen concentration of the crystalgrowth process of Examples 8 to 11 and Comparative Examples 5 to 8 areadjusted in the manner described in Tables 3-10 below. In addition, thecrystal growth process is performed using the first crystal seed in themanner described in FIG. 4 to form silicon carbide crystals. Theevaluation of the basal plane dislocations (BPD), monocrystallineproportion, resistivity, deviation of an uniformity of the resistivity,and bar stacking-fault (BSF) of the obtained silicon carbide crystals ineach of the crystal growth processes are also shown in Tables 3-10.

TABLE 3 Item Example 8 Crystal growth process N = 1 N = 2 N = 3 N = 4 N= 5 N = 6 Monocrystalline  80% >90% >95% >97% >98% >99% proportion ofcrystal seed Size of crystal seed 200 mm 200 mm 200 mm 200 mm 200 mm 200mm (diameter) (i) ratio difference 3 2.8 2.5 2 1.6 0.8 (ΔTz/ΔTx) betweenthe axial temperature gradient (ΔTz) and the radial temperature gradient(ΔTx) (ii) doping Fixed Fixed From low From low From low From lowvariation method of concentration concentration to high to high to highto high the nitrogen concentration (iii) doping 3 × 10¹⁸ 2.9 × 10¹⁸ Low:Low: Low: Low: amount of the greater than greater than greater thangreater than concentration 2 × 10¹⁸ 2.1 × 10¹⁸ 2.2 × 10¹⁸ 2.3 × 10¹⁸(atom/cm³) High: High: High: High: less than less than less than lessthan 2.8 × 10¹⁸ 2.7 × 10¹⁸ 2.6 × 10¹⁸ 2.6 × 10¹⁸ The obtained siliconcarbide crystals and wafers basal plane Less Less Less Less Less Lessdislocations than 200 than 95 than 186 than 178 than 163 than 141(BPD)(amount/cm²) Monocrystalline >90% >95% >97% >98% >99% 100%proportion (%) Resistivity 15~20 15~20 15~20 18~20 18~20 19~20 (mΩ · cm)deviation of an <0.4%  <0.3%  <0.2%  <0.1%  <0.07%  <0.01%  uniformityof the resistivity (% dev) Bar stacking fault 5 3   2   2 2   1   (BSF)(ea/wafer)

TABLE 4 Item Example 9 Crystal growth process N = 1 N = 2 N = 3 N = 4 N= 5 N = 6 Monocrystalline  80% >90% >95% >97% >98% >99% proportion ofcrystal seed Size of crystal seed 200 mm 200 mm 200 mm 200 mm 200 mm 200mm (diameter) (i) ratio difference 2.9 2.5 2 1.8 1.2 0.5 (ΔTz/ΔTx)between the axial temperature gradient (ΔTz) and the radial temperaturegradient (ΔTx) (ii) doping From high From high From high From high Fromhigh From high variation method of to low to low to low to low to low tolow the nitrogen concentration (iii) doping High: High: High: High:High: High: amount of the less than less than less than less than lessthan less than nitrogen 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 2.9 × 10¹⁸ 2.8 × 10¹⁸2.8 × 10¹⁸ concentration Low: Low: Low: Low: Low: Low: (atom/cm³)greater than greater than greater than greater than greater than greaterthan 2.1 × 10¹⁸ 2.2 × 10¹⁸ 2.5 × 10¹⁸ 2.5 × 10¹⁸ 2.5 × 10¹⁸ 2.6 × 10¹⁸The obtained silicon carbide crystals and wafers basal plane Less LessLess Less Less Less dislocations than 197 than 182 than 174 than 168than 155 than 141 (BPD)(amount/cm²)Monocrystalline >90% >95% >97% >98% >99% 100% proportion (%) Resistivity15~20 15~20 18~20 18~20 19~20 19~20 (mΩ · cm) deviation of an <0.35% <0.2%  <0.16%  <0.1%  <0.06%  <0.01%  uniformity of the resistivity (%dev) Bar stacking fault 4   3   3 2   1   1   (BSF) (ea/wafer)

TABLE 5 Item Example 10 Crystal growth process N = 1 N = 2 N = 3 N = 4 N= 5 N = 6 Monocrystalline  80% >90% >95% >97% >98% >99% proportion ofcrystal seed Size of crystal seed 200 mm 200 mm 200 mm 200 mm 200 mm 200mm (diameter) (i) ratio difference 3 2.7 2.2 1.7 1.5 0.6 (ΔTz/ΔTx)between the axial temperature gradient (ΔTz) and the radial temperaturegradient (ΔTx) (ii) doping Fixed Fixed From high From high From highFrom high variation method of concentration concentration to low to lowto low to low the nitrogen concentration (iii) doping 3 × 10¹⁸ 2.8 ×10¹⁸ High: High: High: High: amount of the less than less than less thanless than nitrogen 3 × 10¹⁸ 2.9 × 10¹⁸ 2.9 × 10¹⁸ 2.8 × 10¹⁸concentration Low: Low: Low: Low: (atom/cm³) greater than greater thangreater than greater than 2.2 × 10¹⁸ 2.2 × 10¹⁸ 2.5 × 10¹⁸ 2.5 × 10¹⁸The obtained silicon carbide crystals and wafers: basal plane Less LessLess Less Less Less dislocations than 199 than 185 than 178 than 177than 164 than 144 (BPD)(amount/cm²)Monocrystalline >90% >95% >97% >98% >99% 100% proportion (%) Resistivity15~20 15~20 18~20 18~20 19~20 19~20 (mΩ · cm) deviation of an <0.38% <0.29%  <0.22%  <0.18%  <0.05%  <0.01%  uniformity of the resistivity (%dev) Bar stacking fault 3 2   1   1   1   1   (BSF) (ea/wafer)

TABLE 6 Item Example 11 Crystal growth process N = 1 N = 2 N = 3 N = 4 N= 5 N = 6 Monocrystalline  80% >90% >95% >97% >98% >99% proportion ofcrystal seed Size of crystal seed 200 mm 200 mm 200 mm 200 mm 200 mm 200mm (diameter) (i) ratio difference 2.8 2.6 2 1.9 1.6 0.7 (ΔTz/ΔTx)between the axial temperature gradient (ΔTz) and the radial temperaturegradient (ΔTx) (ii) doping variation From low From low From low From lowFrom low From low method of the to high to high to high to high to highto high nitrogen concentration (iii) doping Low: Low: Low: Low: Low:Low: amount of the greater than greater than greater than greater thangreater than greater than nitrogen 2 × 10¹⁸ 2.1 × 10¹⁸ 2.1 × 10¹⁸ 2.2 ×10¹⁸ 2.2 × 10¹⁸ 2.3 × 10¹⁸ concentration High: High: High: High: High:High: (atom/cm³) less than less than less than less than less than lessthan 3 × 10¹⁸ 2.9 × 10¹⁸ 2.8 × 10¹⁸ 2.7 × 10¹⁸ 2.6 × 10¹⁸ 2.5 × 10¹⁸ Theobtained silicon carbide crystals and wafers: basal plane Less Less LessLess Less Less dislocations than 198 than 189 than 177 than 162 than 155than 145 (BPD)(amount/cm²) Monocrystalline >90% >95% >97% >98% >99% 100%proportion (%) Resistivity 15~20 15~20 18~20 18~20 19~20 19~20 (mΩ · cm)deviation of an <0.28%  <0.21%  <0.16%  <0.12%  <0.09%  <0.01% uniformity of the resistivity (% dev) Bar stacking fault 4 3 2 2 1 1(BSF) (ea/wafer)

TABLE 7 Item Comparative Example 5 Crystal growth process N = 1 N = 2 N= 3 N = 4 N = 5 N = 6 N = 7 Monocrystalline 80% 82% 82% 85% 87% 87% 88%proportion of crystal seed Size of crystal 200 mm 200 mm 200 mm 200 mm200 mm 200 mm 200 mm seed (diameter) (i) ratio 10 9.5 9 8.5 8 7.5 7difference (ΔTz/ΔTx) between the axial temperature gradient (ΔTz) andthe radial temperature gradient (ΔTx) (ii) doping Fixed Fixed From lowFrom low From low From low From low variation method concentrationconcentration to high to high to high to high to high of the nitrogenconcentration (iii) doping 8 × 10¹⁸ 7 × 10¹⁸ Low: Low: Low: Low: Low:amount of the greater than greater than greater than greater thangreater than nitrogen 3.1 × 10¹⁸ 3.1 × 10¹⁸ 3.1 × 10¹⁸ 3.1 × 10¹⁸ 3.2 ×10¹⁸ concentration High: High: High: High: High: (atom/cm³) less thanless than less than less than less than 7 × 10¹⁸ 6.9 × 10¹⁸ 6.8 × 10¹⁸6.5 × 10¹⁸ 6.5 × 10¹⁸ The obtained silicon carbide crystals and wafers:basal plane Greater Greater Greater Greater Greater Greater Greaterdislocations than 3000 than 2800 than 2600 than 2400 than 2250 than 2000than 1880 (BPD)(amount/cm²) Monocrystalline 82(%) 82(%) 85% 87% 87% 88%88% proportion (%) Resistivity 22~27 22~27 22~27 22~27 22~27 22~27 22~27(mΩ · cm) deviation of an >5% >4.5%  >4.4%  >4.3%  >3.8%  >3.7%  >3.8% uniformity of the resistivity (% dev) Bar stacking fault 35 32   36 31   38  22   27  (BSF) (ea/wafer) Item Comparative Example 5 Crystalgrowth process N = 8 N = 9 N = 10 N = 11 N = 12 N = 13 Monocrystalline88% 89% 90% 90% 91% 92% proportion of crystal seed Size of crystal seed200 mm 200 mm 200 mm 200 mm 200 mm 200 mm (diameter) (i) ratiodifference 6.5 5.5 4 3 0.4 0.2 (ΔTz/ΔTx) between the axial temperaturegradient (ΔTz) and the radial temperature gradient (ΔTx) (ii) dopingvariation From low From low From low From low From low From low methodof the to high to high to high to high to high to high nitrogenconcentration (iii) doping Low: Low: Low: Low: Low: Low: amount of thegreater than greater than greater than greater than greater than greaterthan nitrogen 3.5 × 10¹⁸ 3.5 × 10¹⁸ 3.6 × 10¹⁸ 3.7 × 10¹⁸ 3.7 × 10¹⁸ 3.7× 10¹⁸ concentration High: High: High: High: High: High: (atom/cm³) lessthan less than less than less than less than less than 6.5 × 10¹⁸ 6 ×10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 5.6 × 10¹⁸ 5.5 × 10¹⁸ The obtained siliconcarbide crystals and wafers: basal plane Greater Greater Greater GreaterGreater Greater dislocations than 1600 than 1430 than 1200 than 1100than 1100 than 1100 (BPD)(amount/cm²) Monocrystalline 89% 90% 90% 91%92% 93% proportion (%) Resistivity 22~27 22~27 22~27 22~27 22~27 22~27(mΩ · cm) deviation of an >4.8%  >3.8%  >4.3%  >4.5%  >4.10%    >4%uniformity of the resistivity (% dev) Bar stacking fault 33   27   21 35  18   9   (BSF) (ea/wafer)

TABLE 8 Item Comparative Example 6 Crystal growth process N = 1 N = 2 N= 3 N = 4 N = 5 N = 6 Monocrystalline 80% 81% 82% 83% 85% 87% proportionof crystal seed Size of crystal seed 200 mm 200 mm 200 mm 200 mm 200 mm200 mm (diameter) (i) ratio difference 9.8 9.6 9 8.3 8 7.2 (ΔTz/ΔTx)between the axial temperature gradient (ΔTz) and the radial temperaturegradient (ΔTx) (ii) doping variation From high From high From high Fromhigh From high From high method of the to low to low to low to low tolow to low nitrogen concentration (iii) doping High: High: High: High:High: High: amount of the less than less than less than less than lessthan less than nitrogen 8 × 10¹⁸ 7.5 × 10¹⁸ 7 × 10¹⁸ 6.9 × 10¹⁸ 6.8 ×10¹⁸ 6.5 × 10¹⁸ concentration Low: Low: Low: Low: Low: Low: (atom/cm³)greater than greater than greater than greater than greater than greaterthan 3.2 × 10¹⁸ 3.1 × 10¹⁸ 3.1 × 10¹⁸ 3.2 × 10¹⁸ 3.2 × 10¹⁸ 3.2 × 10¹⁸The obtained silicon carbide crystals and wafers: basal plane GreaterGreater Greater Greater Greater Greater dislocations than 3000 than 2800than 2500 than 2300 than 2250 than 2100 (BPD)(amount/cm²)Monocrystalline 81% 82% 83% 85% 87% 87% proportion (%) Resistivity 22~2722~27 22~27 22~27 22~27 22~27 (mΩ · cm) deviation of an >5% >5% >5%>4.9%  >4.9%  >4.8%  uniformity of the resistivity (% dev) Bar stackingfault 38   32   28  22   19  18   (BSF) (ea/wafer) Item ComparativeExample 6 Crystal growth process N = 7 N = 8 N = 9 N = 10 N = 11 N = 12Monocrystalline 87% 88% 89% 90% 90% 90% proportion of crystal seed Sizeof crystal seed 200 mm 200 mm 200 mm 200 mm 200 mm 200 mm (diameter) (i)ratio difference 6.5 5.5 4 3 0.4 0.2 (ΔTz/ΔTx) between the axialtemperature gradient (ΔTz) and the radial temperature gradient (ΔTx)(ii) doping variation From high From high From high From high From highFrom high method of the to low to low to low to low to low to lownitrogen concentration (iii) doping High: High: High: High: High: High:amount of the less than less than less than less than less than lessthan nitrogen 6.5 × 10¹⁸ 6.5 × 10¹⁸ 6 × 10¹⁸ 5.8 × 10¹⁸ 5.8 × 10¹⁸ 5.7 ×10¹⁸ concentration Low: Low: Low: Low: Low: Low: (atom/cm³) greater thangreater than greater than greater than greater than greater than 3.2 ×10¹⁸ 3.6 × 10¹⁸ 3.6 × 10¹⁸ 3.6 × 10¹⁸ 3.7 × 10¹⁸ 3.7 × 10¹⁸ The obtainedsilicon carbide crystals and wafers: basal plane Greater Greater GreaterGreater Greater Greater dislocations than 1800 than 1650 than 1400 than1250 than 1150 than 1100 (BPD)(amount/cm²) Monocrystalline 88% 89% 90%90% 90% 91% proportion (%) Resistivity 22~27 22~27 22~27 22~27 22~2722~27 (mΩ · cm) deviation of an >4.5%  >4.5%  >4% >4% >4.1%  >4.10%   uniformity of the resistivity (% dev) Bar stacking fault 22   18   19 20  22   23   (BSF) (ea/wafer)

TABLE 9 Item Comparative Example 7 Crystal growth process N = 1 N = 2 N= 3 N = 4 N = 5 N = 6 Monocrystalline 80% 82% 82% 83% 85% 86% proportionof crystal seed Size of crystal seed 200 mm 200 mm 200 mm 200 mm 200 mm200 mm (diameter) (i) ratio difference 9.8 9.4 9 8.5 8.3 7.8 (ΔTz/ΔTx)between the axial temperature gradient (ΔTz) and the radial temperaturegradient (ΔTx) (ii) doping variation Fixed Fixed From high From highFrom high From high method of the concentration concentration to low tolow to low to low nitrogen concentration (iii) doping 7.5 × 10¹⁸ 7.5 ×10¹⁸ High: High: High: High: amount of the less than less than less thanless than nitrogen 7.2 × 10¹⁸ 6.7 × 10¹⁸ 6.7 × 10¹⁸ 6.5 × 10¹⁸concentration Low: Low: Low: Low: (atom/cm³) greater than greater thangreater than greater than 3.1 × 10¹⁸ 3.2 × 10¹⁸ 3.3 × 10¹⁸ 3.3 × 10¹⁸The obtained silicon carbide crystals and wafers: basal plane GreaterGreater Greater Greater Greater Greater dislocations than 3000 than 2900than 2650 than 2350 than 2250 than 2100 (BPD)(amount/cm²)Monocrystalline 82% 82% 83% 85% 86% 87% proportion (%) Resistivity 22~2722~27 22~27 22~27 22~27 22~27 (mΩ · cm) deviation of an >4.8%  >4.8% >4.8%  >4.9%  >4.9%  >4.8%  uniformity of the resistivity (% dev) Barstacking fault 39   37   32  27   25   28   (BSF) (ea/wafer) ItemComparative Example 7 Crystal growth process N = 7 N = 8 N = 9 N = 10 N= 11 N = 12 Monocrystalline 87% 88% 89% 90% 90% 90% proportion ofcrystal seed Size of crystal seed 200 mm 200 mm 200 mm 200 mm 200 mm 200mm (diameter) (i) ratio difference 6.8 5.5 5 4.8 4 3.2 (ΔTz/ΔTx) betweenthe axial temperature gradient (ΔTz) and the radial temperature gradient(ΔTx) (ii) doping variation From high From high From high From high Fromhigh From high method of the to low to low to low to low to low to lownitrogen concentration (iii) doping High: High: High: High: High: High:amount of the less than less than less than less than less than lessthan nitrogen 6.5 × 10¹⁸ 6.5 × 10¹⁸ 6 × 10¹⁸ 5.9 × 10¹⁸ 5.8 × 10¹⁸ 5.7 ×10¹⁸ concentration Low: Low: Low: Low: Low: Low: (atom/cm³) greater thangreater than greater than greater than greater than greater than 3.4 ×10¹⁸ 3.6 × 10¹⁸ 3.6 × 10¹⁸ 3.6 × 10¹⁸ 3.7 × 10¹⁸ 3.9 × 10¹⁸ The obtainedsilicon carbide crystals and wafers: basal plane Greater Greater GreaterGreater Greater Greater dislocations than 1800 than 1550 than 1400 than1250 than 1150 than 1100 (BPD)(amount/cm²) Monocrystalline 88% 89% 90%90% 90% 91% proportion (%) Resistivity 22~27 22~27 22~27 22~27 22~2722~27 (mΩ · cm) deviation of an >4.5%  >4.5%  >4.3%  >4.3%  >4.0% >4.0%  uniformity of the resistivity (% dev) Bar stacking fault 26  24   19  16   20  16   (BSF) (ea/wafer)

TABLE 10 Item Comparative Example 8 Crystal growth process N = 1 N = 2 N= 3 N = 4 N = 5 N = 6 Monocrystalline 81% 83% 85% 86% 86% 87% proportionof crystal seed Size of crystal seed 200 mm 200 mm 200 mm 200 mm 200 mm200 mm (diameter) (i) ratio difference 9.3 8 7.8 7 6.8 6.5 (ΔTz/ΔTx)between the axial temperature gradient (ΔTz) and the radial temperaturegradient (ΔTx) (ii) doping variation From low From low From low From lowFrom low From low method of the to high to high to high to high to highto high nitrogen concentration (iii) doping Low: Low: Low: Low: Low:Low: amount of the greater than greater than greater than greater thangreater than greater than nitrogen 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸3.1 × 10¹⁸ 3.4 × 10¹⁸ concentration High: High: High: High: High: High:(atom/cm³) less than less than less than less than less than less than 7× 10¹⁸ 6.8 × 10¹⁸ 6.8 × 10¹⁸ 6.6 × 10¹⁸ 6.5 × 10¹⁸ 6.5 × 10¹⁸ Theobtained silicon carbide crystals and wafers: basal plane GreaterGreater Greater Greater Greater Greater dislocations than 2500 than 2300than 2250 than 2000 than 1800 than 1500 (BPD)(amount/cm²)Monocrystalline 82% 84% 85% 86% 86% 89% proportion (%) Resistivity 22~2722~27 22~27 22~27 22~27 22~27 (mΩ · cm) deviation of an >5% >4.5%  >4%>3.8%  >3.7%  >4.2%  uniformity of the resistivity (% dev) Bar stackingfault 39   38  27   23  27   25   (BSF) (ea/wafer) Item ComparativeExample 8 Crystal growth process N = 7 N = 8 N = 9 N = 10 N = 11Monocrystalline 89% 90% 90% 92% 92% proportion of crystal seed Size ofcrystal seed 200 mm 200 mm 200 mm 200 mm 200 mm (diameter) (i) ratiodifference 5.8 5 4.4 3.8 3.5 (ΔTz/ΔTx) between the axial temperaturegradient (ΔTz) and the radial temperature gradient (ΔTx) (ii) dopingvariation From low From low From low From low From low method of the tohigh to high to high to high to high nitrogen concentration (iii) dopingLow: Low: Low: Low: Low: amount of the greater than greater than greaterthan greater than greater than nitrogen 3.4 × 10¹⁸ 3.5 × 10¹⁸ 3.6 × 10¹⁸3.7 × 10¹⁸ 3.71 × 10¹⁸ concentration High: High: High: High: High:(atom/cm³) less than less than less than less than less than 6 × 10¹⁸ 6× 10¹⁸ 6 × 10¹⁸ 5.6 × 10¹⁸ 5.4 × 10¹⁸ The obtained silicon carbidecrystals and wafers: basal plane Greater Greater Greater Greater Greaterdislocations than 1400 than 1250 than 1150 than 1100 than 1050(BPD)(amount/cm²) Monocrystalline 90% 90% 91% 92% 93% proportion (%)Resistivity 22~27 22~27 22~27 22~27 22~27 (mΩ · cm) deviation of an>3.8%  >4.3%  >4.2%  >4.10%    >4.2%  uniformity of the resistivity (%dev) Bar stacking fault 25   15  18   14   14   (BSF) (ea/wafer)

As can be seen from the experimental results of Examples 8-11 shown inTables 3-6 above, when the ratio difference (ΔTz/ΔTx) is controlledwithin the range of 0.5 to 3, and the doping amount of the nitrogenconcentration is controlled within the range of 2*10¹⁸ atoms/cm³ 5 to3*10¹⁸ atoms/cm³, then no matter how the doping method of the nitrogenconcentration is varied, a B-grade crystal seed (poor monocrystallineproportion) can be grown into an A-grade crystal (monocrystallineproportion of 100%) within 6 times (N=6) of the crystal growth process,and the basal plane dislocations (BPD), the resistivity, the uniformityof the resistivity and bar stacking faults (BSF) can all be controlledwithin an ideal range, for example, the BSF is less than or equal to5/wafer.

In comparison, as can be seen from the experimental results ofComparative Examples 5-8 shown in Tables 7-10 above, if the ratiodifference (ΔTz/ΔTx) between the axial temperature gradient (ΔTz) andthe radial temperature gradient (ΔTx) in each crystal growth process isnot within the above range, and the doping amount of the nitrogenconcentration is outside the above range, then even if the crystalgrowth process has been carried out for 11 to 13 times, it is stillimpossible to make the B-grade crystal seed (poor monocrystallineproportion) to grow to form crystals having a monocrystalline proportionof 100%, and the basal plane dislocations (BPD), uniformity ofresistivity and bar stacking fault results are still poor. Accordingly,it can be understood that the crystal growth method of the embodiment ofthe present disclosure can significantly shorten the time required forforming crystals having a high monocrystalline proportion and a largesize.

Third Example

In the third example, (i) the ratio difference (ΔTz/ΔTx) between theaxial temperature gradient (ΔTz) and the radial temperature gradient(ΔTx), (ii) the doping variation method of the nitrogen concentration,and (iii) the doping amount of the nitrogen concentration of the crystalgrowth process of Example 12 and Comparative Example 9 are adjusted inthe manner described in Tables 11-12 below. In addition, the method asshown in FIG. 5 is performed, whereby a smaller-sized crystal seed isused in a preliminary step (N=0) to expand its diameter to form alarger-sized crystal, and after slicing to form the first crystal seed,the method shown in FIG. 4 is performed by using the first crystal seedto perform the crystal growth process for forming silicon carbidecrystals. The evaluation of the basal plane dislocations (BPD),monocrystalline proportion, resistivity, deviation of an uniformity ofthe resistivity, and bar stacking-fault (BSF) of the obtained siliconcarbide crystals in each of the crystal growth processes are also shownin Tables 11˜12.

TABLE 11 Item Comparative Example 12 Crystal growth process (N = 0) N =1 N = 2 N = 3 N = 4 Monocrystalline 100% 80% 85% 90%     95% proportionof crystal seed Size of crystal seed 150 mm 200 mm 200 mm 200 mm 200 mm(diameter) (i) ratio difference 3 2.8 2.5 2 1.2 (ΔTz/ΔTx) between theaxial temperature gradient (ΔTz) and the radial temperature gradient(ΔTx) (ii) doping variation From low Fixed Fixed From low From lowmethod of the to high concentration concentration to high to highnitrogen concentration (iii) doping Low: 2.8 × 10¹⁸ 2.7 × 10¹⁸ Low: Low:amount of the greater than greater than greater than nitrogen 2 × 10¹⁸2.1 × 10¹⁸ 2.2 × 10¹⁸ concentration High: High: High: (atom/cm³) lessthan less than less than 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ The obtained siliconcarbide crystals and wafers: basal plane Less Less Less Less Lessdislocations than 197 than 186 than 173 than 162 than 144(BPD)(amount/cm²) Monocrystalline  80% 85% 90% 95%    100% proportion(%) Resistivity 15~20 15~20 18~20 18~20 19~20 (mΩ · cm) deviation of an<0.3%  <0.1%  <0.08%    <0.02%    <0.015% uniformity of the resistivity(% dev) Bar stacking fault 200 mm 200 mm 200 mm 200 mm 200 mm (BSF)(ea/wafer) basal plane 5 4   4   3 1   dislocations (BPD)(amount/cm²)

TABLE 12 Item Comparative Example 9 Crystal growth process N = 0 N = 1 N= 2 N = 3 N = 4 N = 5 Monocrystalline 100%  70% 71% 71% 72% 73%proportion of crystal seed Size of crystal seed 150 mm 200 mm 200 mm 200mm 200 mm 200 mm (diameter) (i) ratio difference 8 7.5 6.8 6 5.8 5.05(ΔTz/ΔTx) between the axial temperature gradient (ΔTz) and the radialtemperature gradient (ΔTx) (ii) doping variation From low Fixed FixedFrom low From low From low method of the to high concentrationconcentration to high to high to high nitrogen concentration (iii)doping Low: 4 × 10¹⁸ 5 × 10¹⁸ Low: Low: Low: amount of the greater thangreater than greater than greater than nitrogen 3.5 × 10¹⁸ 5.2 × 10¹⁸5.6 × 10¹⁸ 5.8 × 10¹⁸ concentration High: High: High: High: (atom/cm³)less than less than less than less than 8 × 10¹⁸ 8 × 10¹⁸ 8 × 10¹⁸ 8 ×10¹⁹ The obtained silicon carbide crystals and wafers: basal plane LessLess Less Less Less Less dislocations than 3500 than 3200 than 2800 than2000 than 1800 than 1500 (BPD)(amount/cm²) Monocrystalline 70% 71% 71%72% 73% 74% proportion (%) Resistivity 22~27 22~27 22~27 22~27 22~2722~27 (mΩ · cm) deviation of an <5% <4.9%  <4.5%  <4.2%  <4% <3.5% uniformity of the resistivity (% dev) Bar stacking fault 200 mm 200 mm200 mm 200 mm 200 mm 200 mm (BSF) (ea/wafer) basal plane 34  30   10   97   7   dislocations (BPD)(amount/cm²) Item Comparative Example 9Crystal growth process N = 6 N = 7 N = 8 N = 9 N = 10 Monocrystalline74% 75% 76% 77% 78% proportion of crystal seed Size of crystal seed 200mm 200 mm 200 mm 200 mm 200 mm (diameter) (i) ratio difference 4.46 3.873.28 3.2 3.1 (ΔTz/ΔTx) between the axial temperature gradient (ΔTz) andthe radial temperature gradient (ΔTx) (ii) doping variation From lowFrom low From low From low From low method of the to high to high tohigh to high to high nitrogen concentration (iii) doping Low: Low: Low:Low: Low: amount of the greater than greater than greater than greaterthan greater than nitrogen 6 × 10¹⁸ 6.2 × 10¹⁸ 6.5 × 10¹⁸ 6.5 × 10¹⁸ 6.6× 10¹⁸ concentration High: High: High: High: High: (atom/cm³) less thanless than less than less than less than 8 × 10¹⁹ 8 × 10²⁰ 8 × 10²⁰ 7.8 ×10²¹ 7.5 × 10²¹ The obtained silicon carbide crystals and wafers: basalplane Less than Less Less Less Less dislocations 1200 than 1100 than1000 than 900 than 850 (BPD)(amount/cm²) Monocrystalline 75% 76% 77% 78%79% proportion (%) Resistivity 15~25 15~25 15~25 15~25 15~25 (mΩ · cm)deviation of an <3.2%  <3% <2.8%  <2.8%  <2.5%  uniformity of theresistivity (% dev) Bar stacking fault 200 mm 200 mm 200 mm 200 mm 200mm (BSF) (ea/wafer) basal plane 13    14    6   7   6   dislocations(BPD)(amount/cm²)

As can be seen from the experimental results of Example 12 shown inTable 11 above, when a smaller-sized A-grade preliminary seed(monocrystalline proportion of 100%) is further used for diameterexpansion to form the first crystal seed, and the ratio difference(ΔTz/ΔTx) between the axial temperature gradient (ΔTz) and the radialtemperature gradient (ΔTx) of each crystal growth process is controlledwithin the range of 0.5 to 3, and the doping amount of the nitrogenconcentration is controlled within the range of 2*10¹⁸ atoms/cm³ to3*10¹⁸ atoms/cm³, then no matter how the doping method of the nitrogenconcentration is varied, the smaller-sized A grade crystal seed(monocrystalline proportion of 100%) can be grown into adiameter-expanded large size A-grade crystal (monocrystalline proportionof 100%) within 1 time of preliminary diameter expansion and 4 times(N=4) of the crystal growth process, and the basal plane dislocations(BPD), the resistivity, the uniformity of the resistivity and barstacking faults (BSF) can all be controlled within an ideal range, forexample, the BSF is less than or equal to 5/wafer.

In comparison, as can be seen from the experimental results ofComparative Example 9 shown in Table 12 above, if the ratio difference(ΔTz/ΔTx) between the axial temperature gradient (ΔTz) and the radialtemperature gradient (ΔTx) in each crystal growth process is not withinthe above range, and the doping amount of the nitrogen concentration isoutside the above range, then even if one time of preliminary diameterexpansion and 10 times of the crystal growth process has been performed,it is still impossible to make the small-sized A-grade crystal seed(monocrystalline proportion of 100%) to grow to form larger sizecrystals having a monocrystalline proportion of 100%, and the basalplane dislocations (BPD), uniformity of resistivity and bar stackingfault results are still poor. Accordingly, it can be understood that thecrystal growth method of the embodiment of the present disclosure cansignificantly shorten the time required for forming crystals having ahigh monocrystalline proportion and a large size, thus the multipleexpansion steps and years of expansion time required for traditionalcrystal size expansion can be avoided.

In summary, the N-type silicon carbide crystals formed by the method ofgrowing silicon carbide crystals of the embodiment of the presentdisclosure can have a uniform resistivity distribution. Accordingly, thecrystal stress of the formed silicon carbide crystals is also lowered,and the geometry of the processed wafer is also improved. In addition,through the crystal growth method of the embodiment of the presentdisclosure, the time to form a large-sized crystal with a highmonocrystalline proportion can be greatly shortened, and crystals havingexpanded diameter and/or with 100% monocrystalline proportion can beachieved within a certain number of crystal growth processes.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed embodimentswithout departing from the scope or spirit of the disclosure. In view ofthe foregoing, it is intended that the disclosure covers modificationsand variations provided that they fall within the scope of the followingclaims and their equivalents.

What is claimed is:
 1. A crystal growing method for crystals,comprising: providing a first crystal seed, wherein the first crystalseed has a first monocrystalline proportion and a first size; performingN times of crystal growth processes on the first crystal seed, whereineach of the crystal growth process will increase the firstmonocrystalline proportion, and the N times of crystal growth processesare performed until a second crystal having a monocrystalline proportionof 100% is reached, and wherein the N times includes more than 3 timesof crystal growth processes.
 2. The method according to claim 1, whereineach of the N times of crystal growth processes comprises adjusting aratio difference (ΔTz/ΔTx) of an axial temperature gradient (ΔTz) and aradial temperature gradient (ΔTx) of the crystals to control the ratiodifference within a range of 0.5 to 3 for forming the second crystal. 3.The method according to claim 1, wherein each of the N times of crystalgrowth processes comprises: using a previously obtained crystal seed forcrystal growth to obtain an intermediate crystal with increasedmonocrystalline proportion; and when it is confirmed that themonocrystalline proportion of the intermediate crystal is not 100%, theintermediate crystal is sliced to obtain a growth crystal seed, whereinthe growth crystal seed is used as a crystal seed for a subsequentcrystal growth process, and when it is confirmed that themonocrystalline proportion of the intermediate crystal reached 100%, thecrystal growth processes are stopped and the second crystal is obtained.4. The method according to claim 1, further comprising: providing apreliminary crystal seed, the preliminary crystal seed has a size A anda monocrystalline proportion A′, wherein the size A is smaller than thefirst size, and the monocrystalline proportion A′ is larger than thefirst monocrystalline proportion; using the preliminary crystal seed toperform a crystal growth process to obtain a first crystal having thefirst size and the first monocrystalline proportion; and slicing thefirst crystal to form the first crystal seed.
 5. The method according toclaim 1, wherein the N times includes more than 3 times and less than 8times of crystal growth processes.
 6. The method according to claim 1,wherein the N times includes more than 4 times and less than 6 times ofcrystal growth processes.
 7. The method according to claim 6, whereineach of the crystal growth processes has different processingconditions.
 8. The method according to claim 7, wherein each of thecrystal growth processes has a different ratio difference (ΔTz/ΔTx) ofan axial temperature gradient (ΔTz) and a radial temperature gradient(ΔTx) of the crystals, or different doping amounts of a nitrogenconcentration.
 9. The method according to claim 1, wherein each of thecrystal growth processes comprises controlling a doping amount of thenitrogen concentration in a range of 2*10¹⁸ atom/cm³ to 3*10¹⁸ atom/cm³.10. The method according to claim 1, wherein the first monocrystallineproportion is 70% to 80%.
 11. The method according to claim 1, whereinthe first size is 200 mm.